[James-T]

I'm sure I can find that info somewhere here but it never hurts to ask fresh. The amp is totally stock and my tech is telling me (along with the tone) that the 40 year old caps are shot.

What other simple things could I get him to do at the same time and what caps and tubes should I order and from where?

Help would be greatly appreciated!

Peace,

James

[tatittle]

My amateur understanding is that big caps (like in the doghouse hanging below the chassis) electrolytics, definitely do wear out over time, but that others like the tone caps (I forget the proper term; linking caps or something to that effect) do not age badly usually. How much they drift varies widely, and Ive heard that lack of use is actually a higher risk of aging the caps faster. The tone will certainly be different with old drifting caps, but the real danger I believe is when they start leaking and risk causing bigger problems like blown output tranny's. The amp will probably be a lot stronger and better sounding after proper maintainance, especially if the output tubes are weak so it is well worth the time/money, and with a SF there isnt any worry about devaluing its value for resale. As you know components have tolerance variations (e.g. +/- 10%) that I suspect have a bigger (and compounding) affect on the tone than manufacturer for example (at least in the short run). The better caps have tighter tolerances usually. But different construction materials in caps do have different tones I have witnessed.

I think NOS tubes on the other hand can be a step up from the new ones available--although I just saw something about GE manufacturing valves in the USA again. The problem with vintage output tubes is getting strong ones that are matched, they have been picked thru for decades now, like transistors and fuzzes. I have modern JJ's (formerly Tesla) in a Princeton Reverb and Ruby's (Chinese) in a Tremolux and I prefer the tone of the Tremolux greatly. Not sure how much of that is due to the tubes though, but I have heard others give good reviews of the Ruby 6L6GC's in Fender's and AB763's in particular.

If you are using a tech I would be VERY specific about what you want done if you are not close to him and are particular. Techs often get cavalier in servicing amps; rather than just replacing what the amp needs they can just shotgun a whole bunch of stuff at the same time. This inhibits the players ability to know what changes made what difference, and in the case of collectables can destroy a lot of resale value. On the other hand it will cost a lot less to have everything done while he has the amp open--modifications for example.

[tatittle]

I would certainly have him add a bias adjustment pot. A little pot inside the chassis is good enough, many guys do this standard. This will make changing tubes (matched) easier in the future. I think a '73 Twin has the "hum balance" pot on the rear which I think was a misguided compromise (replacing the old bias) for the lack of matched tubes back in the day. A true bias pot will allow you to experiment with different settings to suit your taste as well.

Another idea Ive heard that sounds promising is putting a switchable pot in the Tremolo (vibrato) so that you can bypass that part of the circuit entirely when not in use, preventing loss of signal there. Oh yeah, a pre-amp out is terrific too. Finally there are mods that knowledgable folks have deduced were likely done to Jerry's Twin that are not too elaborate. I even heard chatter about the possibility one of these guys might consider doing them himself. Mailing a chassis to a qualified and caring tech is well worth the extra expense and time, especially if you are not familiar with the techs in your area.